1. Field of the Invention
The present invention relates to a system for transferring bobbins from and to a textile machine provided with a plurality of spindles, such as a ring spinning frame or a ring twisting frame.
2. Description of the Related Arts
In a ring spinning frame, a bobbin exchanging operation is necessary at the stage of doffing cops formed on spindles, in which first, a plurality of empty bobbins are arranged along a row of spindles so that each empty bobbin is positioned in front of the respective spindle, and then full bobbins (cops) on the spindles are exchanged with the empty bobbins by an auto-doffer. Removal of the doffed full bobbin from the spinning frame and preparation of the fresh empty bobbin thereto are generally carried out by a common conveyor comprising a steel belt extending on each side of the spinning frame and driven by a pair of pulleys provided on both ends of the belt. The steel belt carries a plurality of pegs for mounting the bobbins thereon, which pegs are secured at an accurate pitch corresponding to a spindle pitch or a half thereof so that an exact correspondence between the peg and the spindle is obtained when the doffing operation is carried out. The steel belt, however, has a serious drawback of elongation during use, which causes the peg pitch to increase. Under such circumstances, the pegs deviate from the desired positions due to an accumulation of pitch errors, and thus the doffing operation is hindered thereby.
To solve the above problem, a bobbin transferring apparatus without a steel belt was proposed, for example, in Japanese Unexamined Patent Publication (Kokai) No. 57-161133. According to this apparatus, as illustrated in FIGS. 16 and 17, a plurality of disc-like trays 73 are slidably placed, in series, on a guide rail 72 extending along a row of spindles 74. Each tray has a peg 73a thereon for mounting a bobbin and a circular recess 73b on the underside thereof. The recess 73b is engageable with each of checking elements 75 mounted on a rod 76 at a predetermined distance from each other. The checking element 75 is reciprocally movable together with the rod 76 along the guide rail 72 by the action of a cylinder 77, so that the tray 73 moves forward during the forward displacement of the checking element due to the engagement of the checking element 75 with the recess 73b of the tray 73 but remains in the forward position during the backward displacement of the checking element 75 due to the disengagement of the checking element 75 from the recess 73b. Repetition of the above movement causes the tray 73 to advance sequentially along the guide rail 72.
According to the above apparatus, the tray 73 has a diameter identical to the spindle pitch so that the peg pitch corresponds to the spindle pitch when the pegs are positioned in front of the spindle row in a such a manner that the respective tray is brought into contact with the adjacent one. The present available spinning frame generally has about 200 spindles or more in the respective side thereof. If the manufacturing tolerance of each tray is 0.1 mm, the total error for 200 trays may amount to 20 mm over the row, and this will hinder the smooth doffing operation. To eliminate the inconvenience caused by the accumulation of manufacturing errors of the tray, the above apparatus is provided with a plurality of checking elements 75 at a predetermined distance, as stated before, so that a relatively less number of trays are displaced, as one group, by the respective checking element. According to this group displacement, the effective total error for all the trays is divided into the respective groups and can be minimized. In this connection, the following formula must be satisfied for the smooth doffing operation: EQU .DELTA..gtoreq..DELTA.D.times.N
wherein .DELTA.A stands for an allowance for a grip distance of a bobbin catcher in an auto-doffer; .DELTA.D stands for a manufacturing tolerance of the tray; and N stands for the number of trays in one group.
.DELTA.A is 2 mm in the maximum value for securely gripping the bobbin. While, .DELTA.D is usually 0.3 mm when a plastic tray is used without machining to reduce the manufacturing cost. Therefore, in this case, the number N of trays in one group must be smaller than 6. This means that at least 200/6, i.e., thirty four checking elements 75 are necessary for displacing the trays on one side of the spinning frame. As shown in FIG. 17, the checking element 75 is swingably pivoted on a pin 78 so that it can selectively occupy an operative position at which the tip end of the element 75 is engageable with the recess 73b of the tray 73 and a rest position at which the same allows the tray 73 to pass backward. In other words, the same number of moving mechanisms as that of the checking elements 75 is provided. It is not desirable to provide such a large number of moving mechanisms in the vicinity of a spinning frame in which many flies are floating in the atmosphere, because the flies are liable to enter between the parts of the moving mechanism and render them inoperative unless cleaning and maintenance of the moving mechanism is properly carried out.